The disclosed embodiments relate generally to rotary machines and, more particularly, to sealing systems for interfaces between rotating and stationary components.
Rotary machines, such as centrifugal compressors, often use dry gas seals to limit leakage of a process gas along a rotatable shaft to the atmosphere. Lubricating oil supplied to one or more radial bearings of the rotatable shaft often tend to wick along the rotor shaft and foul the tip surfaces of the dry gas seal. Barrier seals (also referred to as “tertiary seals”) are provided between the dry gas seals and the radial bearing to prevent migration of oil towards the dry gas seals. Typically, the barrier seal includes a pair of seals with a gas flow path provided between the pair of seals. The barrier seals may include labyrinth seals, carbon face seals, metallic brush seals, or the like.
However, the barrier seals do not effectively prevent migration of oil in case of reduced buffer gas flow. For example, the barrier seals do not effectively prevent migration of oil from the bearing to the dry gas seal if the flow under the seals is relatively small compared with the effective clearances of the seals. Moreover, the consumption of the separation gas between the pair of seals is also increased.
Accordingly, there is a need for a sealing system that effectively prevents migration of oil from one or more bearings to the dry gas seal under the various operational conditions of the machine. Also, there is a need for a sealing system that reduces consumption of a separation gas between the pair of seals.